We described in the opening of this chapter and in Investigating Life: Mycorrhizal Fungi Can Replace Fertilizer in Cassava Cultivation the possibility of improving plant nitrogen nutrition by manipulating the environment around the plant, in particular by adding fertilizers and mycorrhizae to the soil. Another approach is to improve the plant’s ability to use this nutrient. Significant progress has been made in developing corn varieties with improved nitrogen use efficiency, using both conventional plant breeding (genetics) and biotechnology. The recent publication of the corn genome sequence will provide useful information about genes involved in nitrogen use. For example, the seed company Pioneer Hi-Bred is developing a strain of corn that produces a more efficient version of the enzyme glutamine synthetase (GS). GS adds ammonia to glutamate to form glutamine, and therefore plays an important role in nitrogen assimilation in plants. The new corn strain uses up to 20 percent less nitrogen fertilizer to produce the same yields as other corn varieties.
As we pointed out at the beginning of the chapter, the manufacture of nitrogen fertilizer by the Haber–Bosch process is expensive, both in terms of energy needed and economic costs. For too many farmers, nitrogen deficiency limits the growth of their crops. At Yale University, a team of chemists led by Patrick Holland is attempting to design a new compound that binds nitrogen from the atmosphere, mimicking the natural process of nitrogen fixation. In nature, nitrogen fixation is catalyzed by the enzyme nitrogenase. Nitrogenase has iron and sulfur atoms where catalysis takes place. Holland’s group has made simple molecules in which N and S are bound, but not too tightly, so that atmospheric N2 binds the complex. Eventually the group hopes to develop a synthetic catalyst to make ammonia on-site at farms, replacing industrial ammonia-generating processes that require high temperatures and pressures.